Deuterium, also called heavy hydrogen, is a stable naturally occurring (0.015%) isotope of hydrogen. A deuteron, the nucleus of deuterium, contains one proton and one neutron, whereas the far more common ‘light’ hydrogen nucleus contains no neutrons. Deuterium can be used as a non-radioactive, stable isotopic tracer since small concentrations of heavy water are nontoxic in most organisms. The adult human body naturally contains deuterium equivalent to the amount in about 5 grams of heavy water. In chemical reactions and metabolic pathways, deuterium behaves similarly to ordinary hydrogen, but it can be distinguished from ordinary hydrogen by its mass, using mass spectrometry or infrared spectrometry.
Owing to its tracer qualities, Deuterium is especially useful in deuterium nuclear magnetic resonance spectroscopy (DMR). Deuterium's nuclear spin properties, which differ from those of light hydrogen usually present in organic molecules, allow deuterated organic compounds to be detected with great sensitivity using DMR. Such compounds, including deuterated water (e.g., HDO), are widely used in studies related to metabolism and the movement of drugs and toxic substances in humans and other animals.
Mitochondria are the organelles of oxidative phosphorylation and are present in nearly all eukaryotic cells. A change in cellular oxidative demand can reduce the metabolic rate of oxygen consumption in a particular tissue. Therefore, the mitochondrial metabolic rate of oxygen consumption has profound implications for human health in relation to mitochondrial disease and disorders.
Magnetic resonance spectroscopy utilizing heavy isotope labeled oxygen, such as 17O-MR, has been used to determine the metabolic rate of oxygen consumption (MRO2). For example, it has been shown that 17O-MR makes it possible to determine directly and non-invasively the metabolic rate of oxygen consumption in a sample via the quantitative measurement of the nascent 17O labeled mitochondrial water. The highly exergonic redox reaction that leads to nascent mitochondrial water provides the energy incorporated in ATP. If the breathing air is enriched in 17O2, the resulting H217O can be quantitatively measured and related to MRO2 (Mateescu and Cabrera, (1997) Adv Exp Med Biol. 411:585-590).
17O-MR constitutes an excellent avenue for monitoring oxygen consumption. However, it would be advantageous to add the possibility of also measuring MRO2 through the influx of protons provided by food (e.g., sugars, fat, proteins, etc.) in order to determine the metabolic rate of oxygen consumption in a sample.